The present invention relates to a disk apparatus of a data surface servo system for use in a disk drive system.
Disk drive systems in various servo systems, such as a magnetic disk drive system comprising a magnetic disk apparatus, a host computer, and a disk controller interconnecting the magnetic disk apparatus and the host computer, are known. A disk drive system in a data surface servo system is one of those known disk drive systems. According to such a data surface servo system, servo data is written in a servo area of a disk for entering data at least during every revolution of the disk. The servo data is used for producing control signals for controlling a positioning servomechanism for aligning a magnetic head with the center of the track.
In a data surface servo system as disclosed, for example, in U.S. Pat. No. 4,396,959, a detector, provided on a spindle motor for rotatively driving a disk, produces an index signal immediately before the servo area. Then, the index signal is applied to the servo controller of the magnetic disk apparatus to produce a write inhibit signal for masking a write gate signal applied by a disk controller to the magnetic disk apparatus during the write operation to protect servo data previously recorded on the data side of the disk. After being delayed by the servo controller, the index signal is applied to the disk controller for producing a write gate signal. Consequently, since the format write operation of the disk controller continues from the moment when the leading edge of the delayed index signal is detected to the moment when the leading edge of the next delayed index signal is detected, the operation of the disk controller is unavoidably inhibited from the end of writing the format on one track to the start of writing the next format, for a latency period corresponding to one revolution.
To eliminate such inconvenience, a write gate signal may be produced by applying to the disk controller index signals produced immediately before and immediately after the servo area, respectively, in the magnetic disk apparatus.
However, known disk controller are incapable of discriminating whether the index signals are those produced immediately before or immediately after the servo area. Accordingly,
known disk controller are unable to be used for producing the write gate signal in such a manner. To provide known disk controllers with an index signal discriminating function, additional circuits in terms of gates, on the order of approximately 600 gates, need to be incorporated into the disk controller, which is a considerable increase in the circuitry.
Thus, a latency period corresponding to one revolution is indispensable in the known disk drive system as disclosed in U.S. Pat. No. 4,396,959 for a format data verify process or for a format write process for the next track, after the end of a format write process for the preceding track in the format mode, and hence the disk drive system requires considerable time for the format process. Even if the disk apparatus is constituted so as always to apply to the disk controller two index signals, immediately before and immediately after the servo area, still known disk controllers are unable to function without requiring a considerable increase in circuitry.